Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-03-23
2001-03-20
Font, Frank G. (Department: 2877)
Coherent light generators
Particular active media
Semiconductor
C372S038060
Reexamination Certificate
active
06205162
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a semiconductor laser device which may be contained in a compact disc player or an optical pickup.
FIG. 4
shows the circuit structure of a prior art semiconductor laser device of this kind with a laser diode
1
contained inside a package
10
, connected through wires or lead lines to its terminals T
1
and T
2
outside for applying a voltage thereacross and thereby providing an optical output according to the applied input voltage.
While there is no source voltage being applied to such a circuit, it sometimes happens that the static electricity of the circuit causes a current (referred to as “a surge current”) to flow through, thereby degrading or destroying the diode because laser diodes are typically much more fragile than ordinary ICs against a surge current.
Since prior art semiconductor laser devices are structured such that the surge current would completely flow into the laser diode, the laser diode is easily degraded or destroyed. In other words, prior art semiconductor laser devices had only a very low resistance against surge currents.
It was necessary therefore to take an adequate measure when a prior art semiconductor laser device was installed in its driving circuit, for example, in order to prevent such degradation or destruction of the laser diode by a surge current. If a circuit for absorbing the surge current is to be attached externally, however, this will increase the total area of the set into which the semiconductor laser device is incorporated.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a semiconductor laser device with improved resistance against surge currents.
A semiconductor laser device embodying this invention, with which the above and other objects can be accomplished, may be characterized as comprising a package containing therein both a laser diode for outputting light according to a voltage applied thereto and a protective element having a control terminal. The protective element is connected in parallel with the laser diode, and its impedance is significantly smaller (say, by one order of magnitude or more) than that of the laser diode when no voltage is applied to the control terminal but is significantly larger (say, by one order of magnitude or more) when a specified voltage is applied to the control terminal. The protective element may be a depletion mode FET of which the drain and the source are connected in parallel with the laser diode and of which the gate serves as the control terminal.
According to a preferred embodiment of the invention, a photoelectric conversion IC for converting a received light signal into an electrical signal is also contained in the same package, containing the protective element therein. Since the photoelectric conversion IC has many terminals, one of them may be used as the control terminal for the protective element. This embodiment is particularly advantageous in the case of a device such as a compact disc player and an optical pickup which requires the existence of a photoelectric conversion IC because its production process can be thereby simplified. The laser diode may be mounted on a base plate which also contains the protective element or the photoelectric conversion IC. A device thus structured is particularly easy to handle, for example, when the operation of the laser diode is checked during the production process.
REFERENCES:
patent: 4506151 (1985-03-01), MacDonald et al.
patent: 5812570 (1998-09-01), Spaeth
patent: 5936270 (1999-08-01), Kamada
patent: 5991134 (1999-11-01), Tan et al.
patent: 4315581 A1 (1994-11-01), None
Coudert Brothers
Font Frank G.
Rodriguez Armando
Rohm & Co., Ltd.
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